The objective of this investigation is to determine the biochemical mechanisms involved in the regulation of replication of one of the smallest known DNA viruses, bacteriophage M13. The origin of replication will be isolated by restriction enzyme cleavage of the duplex replicative form DNA and gel electrophoresis. The origin-containing fragment will be sequenced by the technique of Gilbert and Maxam. In addition, the 5' terminus of the open strand of the M13 RF II will be sequenced by the same techniques. Mini-circular RF molecules of 0.2-0.4 times unit-length will be cloned and characterized with regard to the DNA sequences contained. BIBLIOGRAPHIC REFERENCES: Chen, T.C. and Ray, D.S., "Replication of Bacteriophage M13 X. M13 Replication in a Mutant of Escherichia coli Defective in the 5' yield 3' Exonuclease Associated with DNA Polymerase I", J. Mol. Biol. 106, 589 (1976). Suggs, S.V. and Ray D.S., "Replication of Bacteriophage M13 XI. Localization of the Origin for M13 Single-strand Synthesis", J. Mol. Biol. 110, 147 (1977).